1. Technical Field
The present invention relates to a piezoelectric element, a liquid ejecting head, and a liquid ejecting apparatus.
2. Related Art
Piezoelectric actuators are used in liquid ejecting heads and the like. A typical example of the piezoelectric actuators used for liquid ejecting heads is one driven in a flexural vibration mode.
An example of the liquid ejecting heads is an ink jet recording head or the like including a vibrating plate which constitutes a portion of a pressure-generating chamber communicated with a nozzle orifice which ejects ink droplets so that the vibrating plate is deformed by a piezoelectric element to apply pressure to ink introduced into the pressure-generating chamber, ejecting ink droplets from the nozzle orifice. The piezoelectric actuator provided on the ink jet recording head is formed by, for example, forming a uniform piezoelectric material layer over the entire surface of the vibrating plate and cutting the piezoelectric material layer in a shape corresponding to the pressure-generating chamber by lithography so that the actuator can be driven independently for each pressure-generating chamber.
A piezoelectric element representative of the piezoelectric actuators is formed by depositing in order an adhesive layer, a platinum layer, and an anti-diffusion layer to form a lower electrode on a silicon single-crystal substrate, forming a piezoelectric precursor film composed of a piezoelectric material and firing the film to form a piezoelectric layer including a crystallized piezoelectric film, and depositing an upper electrode (refer to, for example, WO99/45598 (pages 19 to 23, FIGS. 12 to 14).
The performance of a piezoelectric element depends on the performance of a piezoelectric material of a piezoelectric layer. For example, when the piezoelectric material is a compound oxide such as lead zirconate titanate or the like, the durability, leak current characteristics, displacement characteristics, and the like of the piezoelectric element may be controlled by the quality and amount of detects present in crystals of the compound oxide. In addition, it has been found that oxygen atoms tend to separate (oxygen defect) from their original positions in crystals, move toward electrodes which hold the piezoelectric layer therebetween, and accumulate. Further, such oxygen defects may accelerate the formation of lead defects, thereby causing PbO defects. Therefore, when the piezoelectric element having crystal defects is used for a liquid ejecting head of the like, the operation of the piezoelectric element may change with time, causing the problem of changing conditions for ejecting a liquid.
The inventors have found that a relative amount of some specified defects among various defects produced in a piezoelectric layer easily affects the performance of the piezoelectric element. The present invention has been achieved on the basis of this finding.